Subgrade utility vaults are widely used to provide internal enclosed regions where utility connections can be made and housed. Classic examples of such connections are the joining of electrical cables used in street lighting, fiber optic cables in telephone and communication systems, and water valves for residential communities and golf courses. These vaults are generally placed below ground level with their upper surfaces at grade where loads from pedestrians and vehicles, as well as environmental factors such as the precipitation and animals, are anticipated. Generally the vaults will be used by municipalities, utility companies, and homeowners at locations where longevity, durability, and affordability are important criteria.
Prior art vaults typically comprise a lid to enclose a vault and protect the contents of the vault against external loads and environmental conditions. The following references relate to the field of subgrade vaults and facilities and are hereby incorporated by reference in their entireties: U.S. Pat. No. 4,567,697 to Hahne; U.S. Pat. No. 6,772,566 to Machledt et al.; U.S. Pat. No. 6,899,240 to Dang et al.; U.S. Pat. No. 7,163,352 to Jurich et al.; U.S. Pat. No. 7,385,137 to Burke et al.; U.S. Pat. No. 7,467,910 to Lecuyer et al.; and U.S. Pat. No. 7,748,926 to Jurich et al.
External loads are considered in prior art designs since, as noted above, subgrade utility vaults can experience loads from pedestrians or even vehicles traveling over the top of the subgrade utility vault and vault lid. The Society of Cable Telecommunications Engineers (“SCTE”) maintains load standards for utility vaults, including ANSI/SCTE 77 2013, entitled “Specification for Underground Enclosure Integrity,” which is hereby incorporated by reference in its entirety. The ANSI/SCTE 77 2013 standard outlines different load requirements for different applications of a utility vault and lid. Tier 15 and Tier 22 applications include “[d]riveway, parking lot, and off-roadway applications subject to occasional non-deliberate heavy vehicular traffic.” See Table 1, pg. 9. The vertical design loads for Tier 15 and Tier 22 applications are 15,000 lbs and 22,500 lbs, respectively. These design loads are the expected loads on the utility vault with a safety factor of 1.5.
An issue with prior art vaults is that the lid is supported only by a peripheral lip around a perimeter of the lid, and the lid and/or vault may deform, distort, or break in Tier 15 or Tier 22 applications. For example, since the lid rests on a horizontal lip or seat of the vault and the relative position between the lid and the horizontal lip or seat is not fixed or maintained, the center of the lid can deflect downward when a person steps on the lid. The ability of the lid to secure to the vault can become compromised, and any sensitive equipment and expensive commodities within the vault are exposed to damage or theft. Therefore, there is a long-felt but unmet need to provide a subgrade utility vault system, and methods for creating such systems, to improve the structural integrity of the vault system.